There's a rational reason for wanting to bring back Ray Allen, because Bradley's timetable recovery is such that a setback could have him missing the start of the season. If the Celtics get two out of: Jeff Green returning and being effective, one of the better uses in the league of the MLE, or drafting a player who ends up being a reasonable candidate for the NBA All-Rookie team, then there is every reason to think the team can be a contender.
I'm actually more concerned about three-point shooting than I am about rebounding.